fix: sanitize tools for moonshot (#24730)

packages/opencode/src/provider/transform.ts

@@ -1089,6 +1089,21 @@ export function schema(model: Provider.Model, schema: JSONSchema.BaseSchema | JS
   }
   */
 
+  if (model.providerID === "moonshotai" || model.api.id.toLowerCase().includes("kimi")) {
+    const sanitizeMoonshot = (obj: unknown): unknown => {
+      if (obj === null || typeof obj !== "object") return obj
+      if (Array.isArray(obj)) return obj.map(sanitizeMoonshot)
+      // Moonshot expands $ref before validation and rejects sibling keywords like description on the same node.
+      if ("$ref" in obj && typeof obj.$ref === "string") return { $ref: obj.$ref }
+      const result = Object.fromEntries(Object.entries(obj).map(([key, value]) => [key, sanitizeMoonshot(value)]))
+      // MFJS does not support tuple-style `items` arrays; it requires one schema object for all array items.
+      if (Array.isArray(result.items)) result.items = result.items[0] ?? {}
+      return result
+    }
+
+    schema = sanitizeMoonshot(schema) as JSONSchema.BaseSchema | JSONSchema7
+  }
+
   // Convert integer enums to string enums for Google/Gemini
   if (model.providerID === "google" || model.api.id.includes("gemini")) {
     const isPlainObject = (node: unknown): node is Record<string, any> =>